Polyurethane foams which cut off water have been used as water-sealing materials. As a conventional polyurethane foam which cuts off water, a polyurethane foam which has high water cut-off property with a holding time of nine hours or longer under water pressure of 100 mmAq and which has a low density of 15 kg/m3 to 40 kg/m3 has been proposed (PTL 1).
The polyurethane foam having high water cut-off property and a low density contains 80 to 100 parts by mass of a hydroxyl-terminated prepolymer obtained by the reaction of a polyether polyol and an isocyanate per 100 parts by mass of the total amount of the polyol and contains a water repellent containing at least one selected from the group consisting of a polybutadiene polyol, a hydrogenated polyol of a polybutadiene, a polyisoprene polyol and a hydrogenated polyol of a polyisoprene, and the isocyanate index is 100 to 150.
However, the flame retardancy of the conventional polyurethane foam having high water cut-off property and a low density has not been examined, and it has been required to improve the flame retardancy thereof for applications which require low flammability, such as a water-sealing material used at a part in an automobile, an OA device or the like where low flammability is required.
Also, as polyurethane foams with low flammability which are used for buffer materials, acoustic materials and the like, non-halogen types which do not use any halogen compound have been proposed recently from the viewpoint of environmental protection. Non-halogen polyurethane foams with low flammability include a polyurethane foam containing a polyol and a phthalate ester polyol and containing melamine powder having a mean particle size of 0.5 μm or less as a flame retardant (PTL 2), a polyurethane foam containing a phthalate ester-based polyol, a phosphate ester-type flame retardant, melamine powder having a mean particle size of 0.1 to 0.5 μm and a hydrate of an inorganic compound (PTL 3) and a polyurethane foam containing melamine and a condensed phosphate ester-type flame retardant (PTL 4).
However, because the conventional polyurethane foams with low flammability which are used for buffer materials, acoustic materials and the like are not used for the purpose of cutting off water, the water cut-off properties have not been examined.
A polyurethane foam is produced by mixing a foaming agent, a catalyst and a flame retardant with a liquid polyol, further mixing a liquid isocyanate therewith to react the polyol and the isocyanate and foaming the materials. A good cell state is not obtained when the materials are not mixed well, and a foaming failure sometimes occurs. For this reason, to obtain a good foam state, all the raw materials used for a polyurethane foam are preferably liquid.
Accordingly, even though it has been attempted to improve the flame retardancy using a flame retardant which is solid at ordinary temperature and which is used for a polyurethane foam with low flammability (for example, melamine) as a raw material of a conventional polyurethane foam which cuts off water or using a solid flame retardant (for example, melamine) and a liquid flame retardant (for example, a condensed phosphate ester-type flame retardant); the amount of the solid flame retardant used has been limited to obtain a foam with a good foam state, and it has not been possible to obtain both excellent water cut-off performance and favorable low flammability.
Moreover, when a condensed phosphate ester-type flame retardant that is liquid at ordinary temperature was used, the water cut-off property under water pressure of around 50 mmAq did not have any problem, but there was a phenomenon that the water cut-off property deteriorated remarkably under water pressure of 100 mmAq.
Thus, it has been impossible to obtain a non-halogen flame-retardant sealing material which has water cut-off property at 100 mmAq and which passes the flammability test according to FMVSS302 (Federal Motor Vehicle Safety Standard No 302). Also, when a liquid phosphate ester-type flame retardant is used, the increase in its amount for the purpose of improving the flame retardancy results in the deterioration of the fogging property and easily causes cloudiness, in case where the material is compressed with a transparent material such as glass. Thus, it has been impossible to obtain a flame-retardant sealing material with good fogging property.